1. Field of the Invention
The present invention relates to a fine tip and a probe unit which are used in, for example, tunneling current detecting apparatuses, minute force detecting apparatuses and scanning tunneling microscopes, as well as a method of manufacturing such fine tip and probe unit.
Furthermore, the present invention relates to a scanning tunneling microscope which employs the probe unit and a data processing apparatus which performs recording, reproduction or erasure of data using the procedures of the scanning tunneling microscope.
2. Description of the Related Art
In recent years, scanning tunneling microscopes (hereinafter referred to as STMs) capable of directly observing the electron structure of the surface atom of a conductor have been developed (G. Binning et al., Phys. Rev. Lett. 49 (1982) 57), and thus the real space image of the surface structure can be measured at a very high resolution (which is in the order of a nanometer or less) regardless of a single crystalline or amorphous substance. Such STMs utilize the flow of a tunneling current between a metal tip (probe) and a conductive substance which occurs when a voltage is applied therebetween and the metal tip is moved to a distance about 1 nm from the conductive substance. Since this tunneling current is very sensitive to changes in the distance between the metal tip and the conductive substance, and changes exponentially as the distance changes, the surface structure of the real space can be observed at an atomic-scale lateral resolution by scanning the tip in such a manner that the tunneling current is maintained constant. Although such an analysis employing the STM has been limited to conductive materials heretofore, the structural analysis of a thin insulating film formed on the surface of a conductive material is now being done. Also, since the above-described apparatus or means employs a method of detecting a fine current, it has an advantage in that it can observe the medium at low power without damaging it. Also, the above-described apparatus or means is capable of operating in the atmosphere. Thus, an expansion of the STM application is to be anticipated in the near future.
For example, research has been done on the application of the STM techniques to the observation/evaluation of the semiconductor or polymer material at an atomic-scale lateral resolution, to fine processing (E. E. Ehrichs, Proceedings of 4th International Conference on Scanning Tunneling Microscope/Spectroscopy, '89, S13-3) and to recording apparatuses.
Particularly in the field of computer or video data, there has been an increasing demand for large-capacity recording apparatuses. Further, since advances in the semiconductor processing technologies have reduced the size of microcomputers and improved their computational ability, a small recording apparatus has been demanded.
In order to fulfil these requirements, a recording/reproducing apparatus has been proposed, which performs recording or writing of data by changing the work function of the surface of a recording medium. This is achieved by applying a voltage from a transducer comprising a tunneling current generating probe which is present on a driving means at a distance from the recording medium which can be finely adjusted, and which performs reading out of data by detecting changes in the tunneling current caused by changes in the work function.
The STM probe to be employed in the recording/reproducing apparatus has been proposed by, for example, Quate et al of Stanford University. This STM probe employs a fine displacement element (IEEE Micro Electric Mechanical Systems, pp. 188-199, Feb. 1990), and forms a bimorph cantilever in which electrodes and thin piezoelectric films are formed on an open portion formed in a silicon substrate using a known photolithographic process and known film forming and etching technologies. A fine tip for detecting tunneling current is mounted on the free end portion of the upper surface of this cantilever, thereby obtaining excellent STM images.
In order to achieve the surface observation at an atomic- or molecular-scale resolution or a high recording density, the radius of curvature of the distal end portion of the fine tip must be small. Also, from the viewpoint of improving the functioning of a recording/reproducing system, particularly, from the viewpoint of increasing the recording/reproducing speed, simultaneous driving of a large number of tips (a multiprobe) has been proposed. Thus, the plurality of fine probes on the same substrate must have the uniform characteristics, e.g., the same height or the same distal end radius of curvature.
Conventionally, such fine tips are formed by silicon anisotropic or isotropic etching using the semiconductor manufacturing process (such method being disclosed in Japanese Patent Laid-Open No. hei 3-135702). In this fine tip forming method, a trench 114 is first formed in a single crystal silicon 111 by anisotropic or isotropic etching, as shown In FIG. 15. Next, SiO.sub.2 113 or another substance, such as C, SiN or SiC, is coated on the entire surface of the single crystal silicon 111 using the trench 114 as a female die. After the coated film has been patterned in the form of a cantilever 115, the silicon located below the cantilever is removed by etching to obtain a cantilever-shaped probe 116.
Alternatively, as shown in FIG. 16(a), a thin film formed on a substrate 121 is patterned in a circular form, and the substrate is etched using the circular thin film as a mask 122. A tip 123 is formed utilizing the side etching. Alternatively, as shown in FIG. 16(b), a conductive material is deposited obliquely on an inversely tapered resist open portion 124 while a substrate 121 is being rotated, and a tip 123 is formed by the lift-off method.
However, the conventional fine tip manufacturing method shown in FIG. 15 has the following problems:
(1) Since the silicon substrate which acts as the female die of the cantilever-shaped probe is removed by etching in a subsequent process, productivity is reduced and production costs increased. PA0 (2) In an STM probe which is formed by coating a conductive material on the cantilever-shaped probe, coating on the sharp distal end portion of the probe is difficult, making provision of an STM which can stably handle a fine tunneling current difficult. PA0 (3) Since that portion of the single crystal Si, in which a trench is formed, is removed by etching, it is difficult to form an interconnection used to transmit a detection signal obtained by detecting a tunneling current to an amplifying or processing portion. PA0 (a) forming a recessed portion in a surface of a first substrate; PA0 (b) forming a peeling layer on the first substrate containing the recessed portion; PA0 (c) laminating a fine tip material on the peeling layer containing the recessed portion to form a fine tip; PA0 (d) joining the fine tip on the peeling layer containing the recessed portion to a second substrate; and PA0 (e) performing peeling on an interface between the peeling layer and the first substrate or between the peeling layer and the fine tip to transfer the fine tip onto the second substrate. PA0 (a) forming a recessed portion in a surface of the single crystal substrate by crystal axis anisotropic etching; PA0 (b) laminating a fine tip material on the single crystal substrate containing the recessed portion to form a fine tip; PA0 (c) forming plurality of electrodes and plurality of piezoelectric layers which constitute the piezoelectric element on the fine tip on the single crystal substance containing the recessed portion; and PA0 (d) performing crystal axis anisotropic etching on the single crystal substrate to form a cantilever including the fine tip and the piezoelectric element on the substrate.
In the conventional fine tip manufacturing methods shown in FIG. 16, it is difficult to maintain fixed resist patterning conditions or fixed material etching conditions, making it difficult to form a plurality of fine tips having a fixed height or an accurate distal end radius of curvature.